The instant invention relates to curing agents and accelerators for use in latent cured epoxy resin compositions.
Compositions comprising an epoxy resin and a curing agent (also known as a hardener) are known in the art. Many curing agents are reactive with the epoxy resin at room temperature and, therefore, are combined with the epoxy immediately prior to use. Others curing agents, known as latent hardeners, are stable in admixture with the epoxy resin at ambient temperature and effect hardening only when heated to elevated temperature.
U.S. Pat. Nos. 3,519,576 and 3,520,905 disclose using salts of monomeric polyhydric phenols with polyamines as latent curing agents for epoxy resins. U.S. Pat. No. 4,866,133 discloses using a solid solution of a polymeric polyhydric phenol with polyamines for curing epoxy resins. The disclosed polyamines contain at least two amine groups with at least one being a primary amine. U.S. Pat. No. 4,689,390 discloses a latent curing agent prepared by reacting a diamine bearing a tertiary amine and a primary or secondary amino group with a poly-epoxy compound and a phenolic resin or phenolic compounds. A solution of a polyamine adduct with bisphenolic A diglycidyl ether in poly-phenolic resins is described in US Pub No US 2012-0077943 A1. U.S. Pat. No. 7,910,667 discloses a polyphenolic resin solution of a polyurea derivative of a polyamine. WO 2012/000171 discloses heat activated tertiary amine catalysts for use with epoxy resins.
The disclosure of the previously identified patents and patent applications is hereby incorporated by reference.
There exists a need for a lower cost, more efficient latent epoxy curing agent. In particular, there is a need for latent epoxy curing agents which exhibit prolonged storage stability at ambient temperature and cure rapidly at greater than about 100° C. The methods and curing agents cited above suffer from several disadvantages which include high use level, too low cure temperature or precursor amines which are obtained by multi-step processes such as adduction with polyepoxides.